Extensive SARS-CoV-2 testing reveals BA.1/BA.2 asymptomatic rates and underreporting in school children

Abstract

Case underreporting during the COVID-19 pandemic has been a major challenge to the planning and evaluation of public health responses. Inconsistent underreporting can undermine effective risk assessment due to high uncertainty in predicted future scenarios. Underreporting rates have been particularly high among children and youth, given that asymptomatic school children were often considered a less vulnerable population. In January 2022, the Canadian province of Newfoundland and Labrador (NL) was experiencing an Omicron variant outbreak (BA.1/BA.2 subvariants) and public health officials recommended that all students returning to elementary, junior high, and high schools (~59,452 students) complete two rapid antigen tests (RATs) to be performed three days apart. To estimate the prevalence of SARS-CoV-2, we asked parents and guardians to report the results of the RATs completed by K-12 students using an online survey, and to specify the students' school level and if students with positive RAT results had symptoms. When comparing the survey responses with the number of cases and tests reported by the NL testing system, we found that 1 out of every 4.3 (3.1-5.3) positive households were captured by provincial case count, with 5.1% positivity estimated from the RAT results, and 1.2% positivity reported by the provincial testing system. The survey data indicate that a higher percentage of SARS-CoV-2 cases were found in elementary schools, with 62.9% of positive cases (95% CI: 44.3%, 83.0%) reported from elementary school students, and the remaining 37.1% (95% CI: 22.7%, 52.9%) reported from junior high and high school students. Asymptomatic infections were 59.8% of the positive cases, with no significant difference between asymptomatic rates in elementary schools (60.8%) or in junior high and high schools (58.1%). Given the low survey participation rate (3.5%), our results may suffer from sample selection biases, and should be interpreted with caution. Nonetheless, our estimate of the underreporting ratio is consistent with ratios calculated from serology data, and our study provides insights into infection prevalence and asymptomatic infections in school children, a currently understudied population.